Introduction:

Teaching new students the dynamics that govern our planet can be difficult at times. This website is intended to extend our students understanding of the geosciences though laboratory exercises. Please enjoy the selected lab modules, diagrams and images regarding the interesting field of plate dynamics. The state mandates and guidelines are provided at the bottom of the webpage to allow you to check if the lab exercise is applicable with your state curriculum.

Topics:

Each laboratory exercise has an abstract and explanation as to what material will be reviewed. A brief summary of the content can help instructors review before conducting the accompanying lesson plan.

James Hutton:

James Hutton courtesy of The AmericanMuseum of Natural History

James Hutton, considered the father of geology, unfolded an idea that would change the way geologists view our planet. Hutton ascertained that the rocks we see today have undergone many different changes to reach the state we currently observe. The idea of Uniformitarism, in which a natural set of properties and processes governs the end results of our observable environment, was the product of his findings. The contrary mindset was catastrophism. This counter argument was comprised that a series of rare and epic events occurred in order to shape our Earth. Hutton never denied the idea of catastrophic events but insisted that the slow processes Earth succumbed to was the dominant source of change.

Hutton's plutonist theory vastly contradicted the current idea that all rock was formed as a result of a global flood. Specifically Hutton observed the differences in the ages of rock further promoting his ideas of a "rock cycle". When unconformities were observed his overarching explanation derived from the rock cycle explained the outcome. With the exception of extraterrestrial sources of influence all of the observable environments here on earth could be explained by a series of melting and cooling, bending or metamorphism and erosion.

The Rock Cycle:

The rock cycle begins deep below the Earth's surface where liquefied rock or magma reaches extraordinary temperatures and pressures. The superheated rock then breaks through the underlying mantle into Earth's crust typically at divergent plate boundaries.

Granite sample courtesy of The United States Geological SurveyMetamorphic Rock courtesy of Britanica

At this divergent boundary new rock pushes the old rock further and further away form the rift zone. As the rock cools it becomes what is commonly known as igneous rock. Igneous rock is broken into two types, intrusive and extrusive. Intrusive or plutonic igneous rock is cooled at a slower rate below the Earth's surface. Extrusive rock is cooled much quicker as it is exposed to a much cooler, less pressurized environment. The rate and environment of which the igneous rock cools determines the final end result of the process. For fast cooling rock, obsidian or volcanic glass can form. In areas where crystallization or slow cooling occurs granite or gabbro can form.

Metamorphic rock is the result of igneous or sedimentary rock being pushed together under tremendous pressure. It becomes metamorphosed taking on new characteristics either physically or chemically. Wide scale metamorphism is referred as regional metamorphism where large bands of rock, particular prominent in mountain ranges, undergo extreme metamorphism. These bands of rock can differentiate also in texture and color, which is known as foliation. Contact metamorphism occurs when intrusive igneous rock heats up and reorders the crystallized structure forming new metamorphic rock. Metasomatism is a process where an intrusive disconformity reacts with the preexisting metamorphic rock and alters its chemical composition.

It is also important to note that metamorphic rock can be the product of sedimentary rock, which has undergone extensive pressurization. This process is commonly found in geologically old sediment deposits and drainage basins.

Sandstone sample courtesy ofMoorland Schools

Sedimentary rock is the result of weathering and erosion. There are two types of erosion, physical where contact between substances breaks down the less hard substance, and chemical where the composition is broken down through decomposition. The result of this erosion displaces the broken down fragments either down water passages or to lower elevations. These sediments gather and while the individual grains that make up these sediments belong to the parent classification of rock when they fuse under pressure over lengths of time the categorized as sedimentary rock. This process is referred as lithification. Sedimentary rock is comprised of two categories. The first being the product of the weathering of non-organic substances, which result in clastic sedimentary rock. The second category is a result of the decomposed deposits of organic material or biogenic sedimentary rock.

Plate Tectonics:

Divergent Boundary courtesy of Riverdell SchoolsConvergent Boundary courtesy of The United States Geological Survey

Alfred Wegener, meticulous in his search for evidence, postulated that the continents resided on moving "plates" which waxed and waned due to thermal currents underneath them. Tectonic movement or continental drift can be broken up into three categories, divergent, convergent, and transform boundaries.

Divergent boundaries occur where upwelling in the Earth's mantle is prevalent enough to force new magma to breach the Earth's surface. This is the birthplace of oceanic crust. Eventually the bi-product of this production reaches a limit where the outlining older crust collides with preexisting oceanic or continental plate boundaries.

Oceanic crust becomes foliated where stratification separates the denser material from the less dense at subduction zones. This is a product of denser material slipping below the more buoyant continental crust, releasing the less dense constituents due to the high temperatures, continuing them to rise relative to the denser material. This convergent boundary allows the older more dense material to sink back towards the Earth's interior maintaining the relatively constant diameter of the Earth. Convergent boundaries also occur where two plates of low-density silica rock collide. These plates undergo extreme metamorphism as they are both not dense enough to sink below one another.

Transform boundaries such as the San Andreas fault line depicts two boundaries scraping against one another. The massive amount of pressure creates a series of metamorphosed terrain. The release of the pent up energy where neither boundary can continue to move provides the necessary jolt of kinetic energy, of which we experience the sensation of earthquakes.

Evidence for Wegener's hypothesis comes from the similarly rare characteristics of environments that are separated by great distances. Fossils such from the late Paleozoic age have been found on the west coast of Africa and on the East coast of South America. Congruently the foliation and elemental constituents of these regions are similar but could not be the outcome of any other process other than continental drift. The jigsaw of the Earth's plates and the relative movement can be traced backwards in geological time by connecting the rare similarities of both the biological evidence and characteristics of its native rock samples